Effects of moisture content and loading profile on changing properties of bone micro-biomechanical characteristics

Background: Our study explored the influences of hydration conditions and loading methods on the mechanical properties of cortical bones and cancellous bones. Material/Methods: Elastic modulus and hardness of human cortical bones and cancellous bones that contained different moisture levels (20%, 30%, 40%, 50%, and 60%) were measured with nanoindentation with different peak loads and loading rates. Cortical bones with 20% and 60% moisture were tested with 30 nm, 40 nm, and 50 nm peak loads at 6 nm/s, 8 nm/s, and 10 nm/s loading rates, respectively. Cancellous bones with 5% or 40% moisture percentages were tested with 600 μN, 750 μN, and 1000 μN peak loads at 200 μN/s, 250 μN/s, and 333 μN/s loading rates, respectively. Results: Under the same loading condition, specimens with higher moisture contents showed decreased elastic modulus and hardness. Under different loading conditions, the loading modes had little influence on elastic modulus and hardness of cortical bone and cancellous bone with low moisture, but had significant influence on specimens with higher moistures. Conclusions: The elastic modulus and bone hardness were affected by the moisture content and the loading conditions in cortical and cancellous bones with high hydration condition but not in those with low hydration condition.